A conventional method of forming a patterned conductive circuit on a radar antenna, as disclosed in Japanese Patent Application Publication No. 2004-193937A, includes the steps of forming a conductive copper layer on a concave surface of a plastic substrate by chemical plating process, thickening the conductive copper layer by electroplating process, forming an antenna pattern region by laser ablation to remove the conductive copper layer outside of the antenna pattern region, and forming a protective nickel layer on the antenna pattern region of the thickened copper layer by electroplating process. Even though the above-mentioned method can be applied to form patterned conductive circuit on a non-conductive substrate, operating time of a laser ablation machine for removing the conductive copper layer outside of the antenna pattern region may be long, especially for a substrate that is relatively large in size. Long operating time of the laser ablation machine undesirably increases the manufacturing time and the manufacturing cost of the radar antenna.